Underbed thread trimmer and controlled single-operation cam mechanism therefor

ABSTRACT

A single-operation cam mechanism includes a cam body with a cam surface extending along the body from an entrance location to an exit location. A cam follower is retained in a waiting position adjacent a part of the cam body at which the exit location is found. When the cam follower is moved free of the retainer, a spring forces the cam follower to the part of the cam where the entrance location is found. Then, as the cam rotates, the cam surface engages the follower and forces it back through the exit location and past a resilient trap to the waiting position. The trap snaps shut after the follower has been forced past it, and the surface of the trap then prevents the follower from moving back into engagement with the cam surface except by way of the entrance location. In an underbed thread trimmer, a support member for the cam follower engages a pin connected to blade-like members, some of which have hooks, to carry one set of such members to a position in which their hooks engage looptaker thread. Another set of such members is carried by the pin to a different location in which their hook engage a limb of needle thread. The follower is connected to the pin by a support member so that movement of the follower back to its waiting position retracts sets of hooks and draws the threads across separate ledger blades to sever them.

DESCRIPTION BACKGROUND OF THE INVENTION

This invention relates to the field of single-operation cams andparticularly to a cam mechanism in which a cam may be rotatedindefinitely with follower means held in a waiting position until it ismoved out of that position and forced, as by a spring, to travel toanother point on the cam and into engagement there with a cam surfacethat will draw it back to the waiting position. In particular, theinvention relates to an underbed thread trimmer for a sewing machinethat incorporates a single-operation cam to drive hooks into position toengage the needle thread and looptaker thread at separate locations andto draw them back against ledger blades to sever both threadsseparately.

From time to time during a sewing operation, the operator cuts theneedle and looptaker threads to withdraw the material from the sewingmachine for any one of a number of purposes, such as to start a new seamor to begin work on new material. In order to withdraw material from thesewing machine, it is necessary for the needle to be in an elevatedposition, clear of the material being worked on. As a result, the needlethread is usually cut on the upwardly facing surface of the materialbeing sewn. The looptaker thread engages the material from below, andthe material is commonly turned over or withdrawn sufficiently from thestitch-forming region to allow access to the looptaker thread so that itcan be cut on the opposite side of the material from the remaining endof the needle thread.

In order to keep the final stitches tight, it is common practice tobackstitch before severing the threads. Alternatively, or in addition,after the threads have been severed one of them can be drawn through thematerial so as to be on the same side as the other thread, and the twoends can then be tied together to prevent any of the stitches fromloosening.

Severing the threads by hand is undesirable in industrial sewing inwhich speed is frequently the most important consideration. As a result,industrial sewing machines frequently include a built-in trimming devicethat can be actuated whenever the operator desires to sever the threads.The most convenient locations for such severing, or trimming, devices isbeneath the bed of the machine to sever the threads between the bed andthe looptaker. Such devices have come to be known as underbed threadtrimmers.

In industrial operations, the need for a high production rate makesmanual tying of the severed threads too costly, and backstitching or theformation of a tack is used to hold the final stitches tight.Furthermore, it is desirable in industrial sewing to sever the threadsas close to the material as possible to keep from wasting thread and tokeep from having to trim the thread ends after they have been severed bythe underbed mechanism. As a result, underbed thread trimmers onindustrial sewing machines normally cut both threads at the same timeand as close as possible to the material being worked on.

It is necessary to trim both the needle and loop-taker threads in such away that there will be a sufficient length of thread to initiate thenext stitching operation. The needle thread must not be trimmed so closeto the needle or with the needle at such a location in its reciprocatingcycle that the thread will be pulled out of the eye of the needle as theneedle continues its cyclic motion.

A further problem associated with the provision of underbed threadtrimmers is that of finding enough space for the mechanism. In the caseof cyclic industrial sewing machines designed from the beginning withthe recognition that underbed thread trimming mechanism will have to beincorporated, space to accommodate the mechanism can be reserved fromthe very beginning. Consumer sewing machines to be operated in the homeare not usually as specialized as industrial machines and are likely toinclude a lot of mechanism that is not used in every sewing operation.Thus, an underbed thread trimmer for a consumer sewing machine mustcompete for space within the housing of the machine with otherstitch-forming apparatus.

In my prior thread trimming mechanism shown and claimed in U.S. Pat. No.3,386,402, the looptaker was a rotary hook with a bobbin in it and themain part of the trimming mechanism was separated from the stitchforming mechanism. In addition, another hook was arranged to grasp boththe needle and bobbin threads at the same time and in the same location.Other underbed thread trimming devices are described in the followingU.S. Pat. Nos.: 3,173,393; 3,359,933; 3,602,170; 3,605,664; 3,709,176;3,776,161 and 3,921,554. None of the foregoing patents has asingle-operation cam, as that term is used herein, and each of thepatents provides means to bring both the needle thread and the looptakerthread into one place to be severed simultaneously by the cutting edgeof a blade, either alone or acting in a scissoring action with a secondblade at the same location.

OBJECTS AND SUMMARY OF THE INVENTION

It is one of the objects of this invention to provide an improvedsingle-operation cam structure.

Another object of the invention is to provide an underbed threadtrimming mechanism incorporating the improved single-operation camstructure.

A further object is to provide an underbed thread trimmer incorporatingmeans to cut the looptaker thread and needle thread at separatelocations.

Yet another object of this invention is to provide underbed threadtrimming mechanism suitable for use in a general purpose sewing machine.

A further object of this invention is to provide an underbed threadtrimmer that will fit into space available in a consumer sewing machinecapable of performing a variety of stitching operations.

Still further objects will become apparent from the followingspecification, together with the drawings.

In accordance with the present invention, a single-operation camarrangement includes a cam body that has a cam surface and is mounted onan axle for rotation. The cam surface has an entrance end and an exitend, and the cam arrangement includes a follower and means to urge thefollower to the entrance end of the cam surface and into engagement withthe latter at that location. The follower is drawn along the cam surfaceby rotation of the cam and passes through an exit trap at the exit endof the cam surface. This trap prevents the follower from returning tocontact with the cam surface until a single operation is desired. Thesingle operation is initiated by moving the cam follower beyond the edgeof the trap to allow the follower to be moved to the entrance end of thecam by a spring, for example.

An underbed thread trimming mechanism according to the present inventionincludes the single-operation cam arrangement with separate hooksconnected to the cam follower to be moved thereby from a waitingposition beyond the trap at the exit end of the cam surface, where thefollower can remain for as long as the machine operator desires, and isthen to be moved relatively quickly, along with the cam follower, to theentrance and to extend the hooks into position to intercept, separately,needle and looptaker threads at specific points in a stitch cycle.Afterwards, the hooks are moved back to a retracted, waiting position asthe cam follower is drawn along the cam surface back to the exit end ofthe cam and past the trap to the waiting position. As the hooks areretracted, they draw the needle and looptaker threads against separateledger blades to sever the threads at different locations and to leavesufficiently long thread ends extending from the work material to makeit possible for the ends to be ties in a knot to keep the stitches frombecoming loosened.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of one embodiment of a singleoperation cam arrangement according to this invention;

FIG. 2 is an exploded, perspective view of thread hooks and ledgerblades and a support structure for them;

FIG. 3 is a perspective view of the main components of an underbedthread trimmer with some of the parts broken away to clarify therelative positions of internal components;

FIG. 4 is an enlarged view of part of the actuator mechanism for theunderbed thread trimmer in FIG. 3;

FIG. 5 is a simplified schematic drawing of an electrical circuitsuitable for use with the underbed thread trimmer in FIGS. 3 and 4;

FIG. 6 shows part of a sewing machine from below to illustrate the waythe underbed thread trimming mechanism of FIG. 3 may be incorporatedinto the machine;

FIG. 7 is a cross-sectional view along the line 7--7 in FIG. 6 of afragment of the sewing machine incorporating the underbed threadtrimmer; and,

FIG. 8 shows the top of the same fragment of the sewing machine as inFIG. 6 with parts broken away to make the interior visible.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows one form of single-operation cam arrangement that includesa helical track 11 along the cylindrical surface 12 of a cam body 13. Anaxle 14 coaxial with the cylindrical surface 12 supports the cam and isrotated by means not shown in FIG. 1. A cam follower suitable for usewith the cam 13 includes a pin 16 that fits in the track 11 to engagethe camming surface 17, which is one of the walls of the slot, and isheld by a support member 18. The support member is also indicated inseveral other positions 18a-8d, but only in dotted lines. The camfollower is indicated in dotted lines in corresponding positions 16a-16dand in an additional position 16e in which the support member is notshown for the reason that the support member would obscure an importantelement of the cam arrangement in that position.

The element that would be obscured is a resilient trap 19 that is partof a resilient member 21 attached to one end of the cam 13 by means of ascrew 22. The resilient member 21 is an annular disc of thin, springsteel having an outer diameter equal to the diameter of the cylindricalsurface 12 of the cam 13 and having an inner diameter at least largeenough to fit loosely over the shaft 14. The resilient member 21 has aslot 20 that extends generally radially from the outer edge of theresilient member to the inner edge. Preferably, this slot is formed insuch a way as to have sloping surfaces 23 and 24, but if the member 21is thin enough, the surfaces that define the slot need not slope. Theresilient member is placed on the end of the cam 13 so that the slopingsurface 24 forms an extension of the camming surface 17 or is displacedangularly therefrom in the direction in which the cam would be rotatedto drive the follower 16 into contact with the trap 19, as shown inposition 16e.

When the axle 14 is so rotated, which would be clockwise as viewed fromthe axle toward the resilient member 21 in this embodiment, with thefollower in position 16e, where it is just about to move through theslot 20, the camming surface 17 forces the follower axially against thetrap. Continued pressure produced by continued rotation of the shaft 17pushes the trap 19 outwardly far enough to allow the follower 16 to movealong the surface 24 to the outer surface 26 of the resilient member 21.As the axle 14 continues to rotate, the resilient trap 19 snaps backflat against the end surface of the cam 13. The axle 14 can continue torotate as long as may be desired, during which time the cam follower 16cannot pass back through the trap to re-enter the track 11 nor beinfluenced by the cam 13 in any way.

The cam follower 16 moves only longitudinally and radially with respectto the cam 13, but in order to illustrate the relative positions betweenthe follower 16 and the track 11, the follower is shown in severalpositions that could only be reached by angular movement around the cam.Thus, although the cam follower 16 can only move back and forth alongthe path indicated by an arrow 27, its waiting position indicated infull lines, adjacent a first part of the cam body is shown displaced 90°around the cam from the illustrated location of the arrow and with thefollower against the surface 26.

The support member 18 is shown in its corresponding waiting positionpulled against the end of the cylindrical surface 12 and against theouter edge of the resilient member 21 by a spring 25. This spring exertsforce that urges the support member toward the opposite end of the cam13 and toward the axis of the cylindrical surface 12. As long as thedistance between the edge of the resilient member 21 and the point onthe head of the screw 22 farthest from the axis of the surface 12 isgreater than the axial length of the follower 16, there will be nointerference between the follower and any part of the rotating cam 13when the follower is in the waiting position.

The follower 16 is actuated to carry out a cycle of operation by simplymoving the support 18 radially outwardly from the waiting positionsufficiently to allow the tip of the follower to clear the outer edge ofthe resilient member 21. This allows the spring 25 to pull the supportmember and the follower toward a remote part of the cam body, i.e., theopposite end of the cam 13. As the support member and the cam followertravel longitudinally along the cam 13, the support member must beradially spaced from the axis of the cam at least as far as is indicatedby the support member position 18a. In this position, the cam followeris in the position 16a, which allows it to slide longitudinally alongthe cylindrical surface 12. It must be kept in mind that, at all times,the follower 16 is constrained to move along the path identified by thearrow 27 and cannot actually move around the cam 13 to the positionsindicated by reference numerals 16 or 16a-16d, for example.

The spring 25 must have enough stored force to move the support memberquickly so that the cam follower cannot drop into the track 11, forexample at the position 18d, as it moves along the surface 12. Thesupport member must not move radially inwardly until it reaches theposition 18b at the opposite end of the cam 13, at which time it canmove radially inwardly so that the bottom of the cam follower in thelocation 16b can engage a generally spirally shaped surface 28 thatleads into the track 11. It will be noted that the depth of the surface28 relative to the surface 12 when the relative angular position betweenthe cam 13 and the follower is that shown in the position 16b is lessthan the full depth of the track 11. However, the surface 28 spiralsdown to the depth of the track 11 at the entrance end of the track.

The entrance portion of the track 11 has a funnel shape as provided by asurface 29. The support member is constrained so that it will not movefarther to the left than is shown in the position 18b, and thus, whenthe cam 13 rotates clockwise, the surface 29 forces the follower 16 tomove into the track 11. The position 18c of the support member and 16cof the follower corresponds to the position of the follower and supportmember shortly after entering the track 11 and being forcedlongitudinally toward the right against the force of the spring 25.

The track 11 shown in FIG. 1 makes only a single turn in passing fromone end of the cam 13 to the other, and the support member position 18dand cam follower position 16d are half a turn apart. A single turn camis desired when the cam is to be used to control the operation of anunderbed thread trimmer for a sewing machine but should not beconsidered as a basic limitation on the cam. It would be possible forthe pitch of the track 11 to be greater or less than is shown so thatthe cam 13 could make less than or more than one turn in driving thefollower longitudinally from the lefthand end of the cam 13 back to theright-hand end.

After the follower has been drawn back along the track 11 past position16e and has emerged through the slot 20 between the surfaces 23 and 24of the resilient member 21, it can return to remain in the waitingposition at the righthand end of the cam while the shaft 14 rotates foran indefinite period of time. However, once the support is liftedradially away from the axis of the surface 12 to allow the follower toclear this cylindrical surface, the follower 16 will move in aconstrained manner as determined by the camming surface 17 and therotation of the cam 13 to complete another single operation of the typejust described.

The cam structure in FIG. 1 is especially useful as part of an underbedthread trimming device for a sewing machine, particularly a consumersewing machine. FIG. 2 shows hooks and cutting ledger blades to snareand cut thread in an underbed thread trimmer. These hooks and bladeswill first be described independently of their relationship to othercomponents of a sewing machine. In FIG. 2, the support member 18 has anend 31 with a slot 32 in it. The end 31 extends through an elongatedslot 33 in a guide structure 34 that has a longitudinal guide slot 36.Flat, blade-like members 37-45 fit in the guide slot 36 andsubstantially fill it up. They are held in place by a top plate 47attached to the guide structure 34 by means of four screws 48 that fitinto threaded holes 49 in the guide structure. The uppermost blade-likemember 45 has a pin 51 rigidly attached to it and extending down throughopenings in all of the other blade-like members 37-44 and through a slot52 that extends axially along the center of the bottom surface 53 of theguide structure 34. The support member 18 is journalled on a shaft 54that allows the support member to move freely in the longitudinaldirection of the shaft to establish the path indicated by the arrow 27for the cam follower 16 in FIG. 1. The pin 51 fits into the slot 32 inthe end of the support member 18 to be moved longitudinally along theguide slot 36 by movement of the support member 18 along the shaft 54between the position shown in full line and the position 18' shown inthe dotted lines. The cam follower 16 is located at the opposite end ofthe support member from the end 31.

The path of movement of the end 31 of the support member 18 isillustrated by a closed loop of arrows starting at a point 55 thatcorresponds to the waiting position of the support member 18 as shown inFIG. 1. In accordance with the description of operation of the cammechanism in FIG. 1, the first step of movement of the support member isto move radially away from the axis of the shaft 14 sufficiently toallow the cam follower 16 to clear the edge of the resilient member 21.This movement of the support member 8 is illustrated in FIG. 2 by anarrow 56 that begins at the point 55 as the support member pivots aboutthe shaft 54, which causes the end 31 to move perpendicularly away fromthe guide member 34 but not far enough to allow the pin 51 to becomedisengaged from the slot 32.

As soon as the cam follower 16 (FIG. 1) clears the perimeter of theresilient member 21, the support member 18 is free to slide to the otherend of the cam 13 quickly and without stopping and then to be pulledradially inwardly with respect to the cylindrical surface 12, all underthe force of the spring 25 in FIG. 1. This motion is indicated in FIG. 2by the long arrow 57 that starts from the end of the arrow 56 andextends parallel to the longitudinal direction of the guide member 34for a distance corresponding to the length of the cam 13 in FIG. 1, atwhich point the arrow 57 bends at a right angle toward the guide member34. The position 18' of the support member 18 is illustrated at thepoint at which the path of movement indicated by the arrow 57 bends.

In FIG. 1, the entrance end of the slot 11 picks up the cam follower 16and forces it back to the end of the cam at which the resilient member21 is located. This movement is much slower than the sudden movement ofthe cam follower and support member acting under the force of the spring25 that draws the cam follower and support member away from the end atwhich the resilient member 21 is located. Therefore, in FIG. 2 themovement of the support member 18 from the position 18' back to theoriginal position is indicated by two arrows 58 and 59, which, by theirlength, suggest the relatively slow return motion of the support member18.

The movement of the pin 51 in FIG. 2 is constrained by the slot 52 sothat the pin does not follow motion of the support member 18perpendicular to the longitudinal dimension of the slot but only followsthe motion parallel to the slot. Only certain of the blade-like members37-45 are permitted to move, and their motion is constrained by the slot36 to a direction exactly parallel to the longitudinal direction of theguide member 34. Three of the members 38, 40, 42, and 44 are not allowedto move at all. These members have notches 61-64 that hook onto a rigidpin 66 held in a fixed position on one side of the slot 36 of the guidemember 34. Each of these fixed members has an elongated central slot67-70, respectively, to allow the pin 51 to move freely as the supportmember 18 forces it to move along the slot 52. The members 40 and 44 areonly spacer members that separate the other blade-like members.

The members 41 and 43 have hooks 72 and 73 at their ends, respectively,to engage one of the threads as will be described hereinafter. Forreasons having to do with the operation of the thread trimmingapparatus, it is desirable that the members 41 and 43 slide the fulldistance of the movement of the support member 18. As a result, themembers 41 and 43, which may be called hook members, have apertures 74and 76, respectively, that fit relatively closely around the pin 51 sothat any movement of the pin will cause a corresponding movement of thehook members. In order to keep such movement from being interfered withby the pin 66, both of the hook members 41 and 43 have notches 77 and78, respectively, cut in the corner where the pin 66 is located.

As will be described in more detail hereinafter, the purpose of thehooks 72 and 73 is to engage of the threads and to draw that thread backto be cut by a ledger blade 79 at the end of the fixed member 42, whichmay be called a ledger blade member. In actual use, the blade-likemembers 37-45 are held in surface-to-surface sliding contact with eachother. Thus, the hook members 41 and 43 are each in surface-to-surfacecontact with the ledger blade member 42. By pulling a thread with bothof the hooks 72 and 73 on opposite sides of the ledger blade 79, thevery short part of the thread between the hooks, the length of whichpart is no greater than the thickness of the ledger blade 79, is heldtaut so as to be easily cut by the ledger blade. The forwardmostposition of the hook members 41 and 43, when they are extended to engagea thread, is illustrated in dotted lines.

For reasons having to do with the operation of the sewing machine, andas will be described hereinafter, the blade-like members 37 and 39 neednot move as far as the hook members 41 and 43 and the members 37 and 39thus have slots 80 and 81 to permit some relative motion between the pin51 and the blade-like members 37 and 39. However, these slots are not aslong as the slot 52, and therefore, when the pin 51 is moved the fulldistance of motion of the support member 18, the blade-like members 37and 39 will at least move from the position shown in full lines to theposition shown in broken lines. These blade-like members have off-setarms 82 and 83, respectively, and they have hooks, or notches, 84 and86, respectively. When these members are extended, the notches occupythe positions indicated in dotted lines to engage a limb of the needlethread to pull it toward a ledger blade 87 at the end of an arm 88off-set from the main part of the blade-like member 38 and directlyaligned with the arms 82 and 83. As in the case of the hooks 72 and 73,the notches 84 and 86 pull only a short, taut length of thread againstthe ledger blade 87 and cut it by a scissoring action. Also like theblade-like members 41 and 43, the movable blade-like members 37 and 39are provided with notches 89 and 91, repectively, to keep theeblade-like members free of the fixed pin 66.

FIG. 3 shows the elements in FIGS. 1 and 2 located in their respectiveoperative positions close to each other and with additional elementsutilized in an underbed thread trimmer.

The looptaker in this embodiment is a rotary hook 93 and the shaft 54 isa hook drive shaft to drive the rotary hook. The shaft 54 is connectedto the hook by way of two bevel gears 94 and 96, the latter of which isconnected to the hook 93 by a vertical axis shaft 97. The hook 93includes a beak 98 that picks up a loop of needle thread 99 formed, orshed, in close proximity with respect to the beak 98 by means of aneedle 101 in a well known manner.

A bobbin 102 is held in a bobbin case 103 within the hook 93. By wellknown means, the bobbin case 103 is prevented from rotating with thehook 93, but the bobbin 102 is able to rotate to the extent necessary tofeed bobbin thread 104 into proper stitch forming relationship with theneedle thread 99.

The hook 93, the bobbin 102, and the bobbin case 103 are all standardelements of existing sewing machines except for a relatively smallrecess 106 formed in the case 103 in position to receive the ends of thearms 82 and 83 when they are driven forward by means of the supportmember 18.

The blade-like members 37, 39, 41, and 43 are pushed toward the hook 93by the support member 18 acting upon the pin 51 (shown in FIG. 2). Thesupport member 18 is shown in its waiting position with the cam followerpin 16 resting against the resilient member 21. A solenoid 107comprising a coil 108 and an axially movable magnetic plunger 109supplies the force to move the support member 18 out of its waitingposition so that it can travel to the other end of the cam 13 inresponse to the force of the spring 25 (FIG. 1). The plunger 109 isconnected to an arm 111 by means of a pin 112 that extends through aslot 113 at the end of the arm 111. The arm 111 is connected to apivoted member 114 pivotally mounted on a fulcrum 116 held in a part ofthe guide structure 34. A release device 117 is pivotally mounted on anaxle 118 in the pivoted member 114, and a spring within the pivotedmember applies pressure in the direction of the arrow 119 to pivot therelease device 117 toward the support member 18. The release device hasa curved cam follower 121 located in a position to be engaged by thepeak 122 of a cam 123, but only under certain circumstances, which willbe described hereinafter.

The release device 117 has an arm 124 that extends into position toengage the push button 126 of a normally-closed microswitch. For thesake of clarity, the only part of the microswitch shown in FIG. 3 is thepushbutton 126. However, the guide structure 34, has a threaded hole 127to facilitate attaching the microswitch to the guide structure by meansof a screw. The release device also has an arm 128 located between thecam follower 121 and the support member 34, and it has an adjustablestop in the form of a screw 129 threaded into the release device 117 toset the location of the cam follower 121 relative to the cam 123 bycontrolling the position of the release device 117 relative to the frontsurface of the support member 34.

FIG. 4 shows an enlarged view of the components in FIG. 3 closelyassociated with the release device 117. Some of these components areshown partly broken away to illustrate the internal construction. Onesuch component is the pivoted member 114, part of the front of which isbroken away to show the axle 118 that supports the release device 117for limited pivotal movement within the support member 114. A spring 131engages the release device 117 and the pivoted member 114 to applypressure in the direction of the arrow 119 to pivot the release devicecounterclockwise about the axle 118 from the position of the actuatorillustrated in solid lines toward the position illustrated in dottedlines.

The main reason the cam 123 and the shaft 14 are broken away is toillustrate a projection 132 that extends from the release device 117. Inthis embodiment, the projection 132 extends from the edge of the arm128, into contact with the juxtaposed surface 133 of the support member18. The broken-away shaft 14 makes the cam follower 16 visible, also,because the cam follower is in its waiting position. A normally-closedmicroswitch 134, for which the pushbutton 126 is the actuator, ismounted on the guide structure 34 by means of a screw 136 threaded intothe hole 127 shown in FIG. 3.

As may be seen in FIG. 4, when the cam follower 16 and the supportmember 18 are in their waiting position while a seam is being sewn, thebeak 122 of the cam 123 rotates generally in line with the space betweenthe cam follower 121 and the side surface 133 of the support member 18.

FIG. 5 is a simplified electrical circuit diagram of an operatingcircuit for the apparatus in FIGS. 3 and 4. In FIG. 5, the solenoid coil108 is connected in series with a normally open switch 137, which may bea pushbutton switch mounted on the bed of a sewing machine. This seriescircuit is connected across a pair of power supply lines 138 and 139. Acontrol circuit 141 is also connected across the lines 138 and 139 andhas two input circuits, one connected to the microswitch 134 shown inFIG. 4, and the other to a speed control 142, which is usually afoot-operated device. The output of the control circuit 141 is connectedto a motor 143 that drives the sewing machine.

The operation of the release device 117 will be described next withreference to FIGS. 3-5.

When the hook 93 and the needle 101 in FIG. 3 are being operated in thenormal manner to make stitches, the hook shaft 54 rotatescounterclockwise and the shaft 14, which drives the feed mechanism (notshown), rotates clockwise. These shafts can continue to rotateindefinitely to produce as long a seam as may be desired, and while theyare rotating, the release device 117 waits in the position shown.

When a single operation of the cam arrangement is to be carried out inthe manner previously described to cut the threads 99 and 104, theoperator actuates the switch 137 (FIG. 5) to energize the solenoid 107momentarily to cause the plunger 109 to be pulled upwardly from theposition illustrated in FIG. 3. This pivots the arm 111 counterclockwiseabout the fulcrum 116 and pivots the release device 117 in the samecounterclockwise direction, initially.

The projection 132 in FIG. 4 is therefore caused to move forward (i.e.,perpendicularly out of the plane of the drawing and toward the viewer)so that it no longer makes contact with the side surface 133 of thesupport member 18. When this happens, the spring 131 is able to pivotthe release device 117 counterclockwise to the position illustrated indotted lines so that the projection 132 is in front of the lower end ofthe support member 18. This movement of the release device 117 moves thearm 124 away from the pushbutton 126 and allows the microswitch 134 toclose, thereby energizing the control circuit 141 to start the motor143, preferably at a relatively slow speed. Movement of the releasedevice also shifts the cam follower 121 to a position where it is inline with the cam 123. The extent of this pivotal movement of therelease device about the axle 118 is sufficient to bring the edge of thearm 128 against the facing surface 133 of the support member 18.

The switch 137 may be actuated when the hook 93 is at any point in itscycle of operation, but the hooks 72, 73 and 84, 86 must not moveforward until the needle 101 is out of the way. This is accomplished byorienting the cam 123 on its shaft 14, which is driven from the hookshaft 54 by standard gears, so that the peak 122 has a specific positionrelative to the beak 98 of the rotary hook 93. The cam follower 121 isso shaped that, at a specific point during the next rotation of the cam123, its peak 122 will engage the surface of the follower 121, therebyforcing the follower 121 and the rest of the release device 117 to pivotclockwise about the fulcrum 116. The solenoid 107 is no longer energizedand so there is no magnetic force to oppose the pressure of the peak 122forcing the cam follower 121 back away from the shaft 14. Since theprojection 121 is now in contact with the front surface of the supportmember 18, this movement of the release device 117 pivots the supportmember 18 counterclockwise around the shaft 54 and moves the camfollower 16 away from the shaft 14 sufficiently to clear the perimeterof the resilient member 21. When this happens, the support member 18 andthe cam follower 16 are suddenly drawn toward the opposite end of thecam 13 by the force stored in the spring 25 (FIG. 1). The support membercarries the pin 51 along and the pin, in turn, carries the hooks 72 and73 and the notches 84 and 86 to positions adjacent the rotary hook 93 tosnare the threads 104 and 99, respectively, as will be describedhereinafter.

The release device 117 remains pivoted slightly toward the cam 13. Thetrack 11 and the cam 123 are angularly positioned relative to each otherabout the axis of the shaft 14 so that the cam follower 16 is drawn bythe cam surface 17 back through the slot 20 just as the peak 122 of thecam 123 reaches a position where it would engage the cam follower 121 onthe next revolution of the shaft 14. However, the movement of the camfollower 16 causes the surface 133 of the support member 18 to pressagainst the end of the projection 132 and pivot the release device 117clockwise around the axle 118 back to the position shown in FIG. 3.Thus, the cam follower 121 just misses being actuated by the peak 122 asecond time. Instead, the cam follower 16 escapes through the slot 20back to the position shown in FIG. 3, where it can remain as long as maybe desired until the operator again energizes the coil 108 of thesolenoid 107.

When the release device 117 pivots clockwise as the cam follower 16moves out of the track 11 and through the slot 20, the arm 127 of therelease device presses against the pushbutton 126 and opens themicroswitch 134. This turns off the motor 142 and causes the machine tostop, which denotes the end of a single operation of the camarrangement.

FIG. 6 shows the way the apparatus of FIGS. 3 and 4 fits into anexisting sewing machine, specifically a Singer Model 2000. It is to beunderstood that the invention is not limited to incorporation in anyspecific machine.

Only a fragment of the underside of the sewing machine is shown, and inaddition, some of the parts are broken away to reveal components thatwould otherwise be hidden. One of the parts that has been broken away isthe hook shaft 54. This shaft has a gear 144 at one end driven by atiming belt 146. The timing belt, in turn, is driven by the motor 143,which is hidden behind a plate 147.

The pushbutton switch that initiates a cycle of the single operation camarrangement is shown mounted on the underside of the bed 148 of themachine. In this embodiment, the bed 148 is convertible, which meansthat the stitch-forming mechanism in it must be compact enough to fitinto a cylinder bed. Essentially, the bed 148 may be considered to be acylinder bed.

Another gear 149 is rigidly attached to the hook shaft 54 and is meshedwith a gear 151 on the shaft 14. The relative diameters of these gearsis such that the shaft 54 rotates twice as fast as the shaft 14.

The apparatus associated with the cam 13 has been described inconnection with FIGS. 3 and 4 and need not be described again except tosay that the cam 13 is mounted on the shaft 14 between the gear 151 andan eccentric 152. The latter is coupled by linkage means 153 and 154 toa standard feed dog to feed material during the sewing process.

FIG. 7 shows a cross-section of the apparatus in FIG. 6 to illustratethe position of the single operation cam arrangement relative to some ofthe other parts of the machine. As may be seen, the guide structure 34is just under the surface of the bed 148 so that the blade-like memberscan be in the limited space between the bed and the relatively flat,horizontal top of the rotary hook 93 (FIG. 3). Furthermore, the compactarrangement of the blade-like members and the fact that they move backand forth along a narrow path of smaller width than the rotary hookallows the underbed thread trimming mechanism of this invention to fitinto available space in the bed 148 without disturbing the feedmechanism.

FIG. 8 shows a top view of approximately the same part of the machine ofwhich FIG. 6 shows the underside. In FIG. 8, the support member 18 isshown at the opposite end of the cam 13 from its waiting position. As aresult, the hook 73 is shown extended to a looptaker thread engagingposition to snare the looptaker thread 104. The hook 73 extends farenough to engage the bobbin thread even when the sewing mechanism is setto make zig-zag stitches with the widest bight. In addition, the needlethread 99 is shown within the notch 86 at the end of the arm 83. Thenotch 86 extends over adjacent regions of the rotary hook 93 and thebobbin case 103 in the needle thread engaging position of the arm 83.The needle thread engaging position is so far from the path of theneedle 101 that the needle thread will be snared in the hook 86 even ifthe stitch-forming mechanism is set to the widest possible bight. Thisclearly shows the separation between the points at which the two threadsare snared, or engaged, although both of them are engaged at a levelbeneath the bed 148.

The looptaker thread 104 always remains in approximately the sameposition. It emerges from the left side of the bobbin 102, as the bobbinis positioned in FIG. 8, and it passes up through the needle opening inthe throat plate (not shown) to connect with the last stitch formed inmaterial held down against the throat plate in the usual manner.

The needle thread 99, on the other hand, is pulled around the bobbincase 103 by the beak 98 of the hook 93 each time a stitch is formed.This makes it possible to locate the notch 86, and its companion notch84, which is directly beneath it, approximately three-fourths of the wayaround the hook 93 in the counterclockwise direction from the locationat which the needle 101 (FIG. 3) pierces the material in making eachstitch.

When the blade-like members 43 and 39 are drawn back to the right fromthe positions in which they are illustrated in FIG. 8, the hook 73 andthe notch 86 pull the respective threads 104 and 99 against the ledgerblades 98 and 87, respectively, to sever these threads. The length ofthread remaining extending from the needle and from the looptaker aftersevering is sufficient to make it easy to start the first stitch of thenext seam to be sewn. Furthermore, the lengths of needle and looptakerthreads extending from the work material after the threads have beensevered in the positions illustrated for the ledger blades 87 and 98 aresufficient to allow a knot to be tied in those threads to prevent anyloosening of the stitches in the work material. Typically, the threadsextend from the material about two or three centimeters or so.

While this invention has been described in terms of a specificembodiment, it will be understood by those skilled in the art thatmodifications may be made therein without departing from the true scopeof the invention as defined by the following claims.

What is claimed is:
 1. An underbed thread trimmer in a sewing machinecomprising a bed, a needle reciprocatingly driven along a path towardand away from the bed, a needle thread carried by the needle, looptakermeans supported in the bed for seizing a loop of needle thread shed bythe needle, the looptaker means containing a quantity of looptakerthread for concatenation with the needle thread to form stitches, anddriving means for driving the looptaker in synchronism with thereciprocation of the needle, the underbed thread trimmercomprising:looptaker thread engaging means movable between a retractedposition and a looptaker thread engaging position; needle threadengaging means movable between a retracted position and a needle threadengaging position spaced from the looptaker thread engaging position;controllable, single-operation driving means to drive the looptakerthread engaging means from its retracted position to the looptakerthread engaging position and to return the looptaker thread engagingmeans to its retracted position and to drive the needle thread engagingmeans from its retracted position to the needle thread engaging positionto engage the needle thread and to return the needle thread engagingmeans to its retracted position; a first ledger blade located in thepath of movement of the looptaker thread engaging means from thelooptaker thread engaging position to the retracted position of thelooptaker thread engaging means to sever the looptaker thread; and, asecond ledger blade located in the path of movement of the needle threadengaging means between the needle thread engaging location and theretracted position of the needle thread engaging means to sever theneedle thread at a point remote from the reciprocating path of theneedle.
 2. The underbed thread trimmer of claim 1 in which the bedcomprises a planar region surrounding the path of the needle, thelooptaker comprises a rotary hook with a vertical axis, and the underbedthread trimmer comprises, in addition, guide means to guide the movementof the looptaker thread engaging means and the needle thread engagingmeans to constrain the movement of both of the engaging means to besubstantially parallel to the planar region of the bed and between thebed and the proximal surface of the rotary hook.
 3. The underbed threadtrimmer of claim 2 in which the guide means comprises parallel straightwalls defining a straight slot, and both the looptaker thread engagingmeans and the needle thread engaging means are constrained to slide onlylongitudinally in the slot.
 4. The underbed thread trimmer of claim 3 inwhich the bed of the machine is a cylinder bed and the guide meansconstrains the thread engaging means to slide in the longitudinaldirection of the cylinder bed.
 5. The underbed thread trimmer of claim 3in which the looptaker thread engaging means, the needle thread engagingmeans, and both of the ledger blades comprise blade-like members withguide portions of substantially equal width, and the guide means isrigidly attached to the bed and the distance between the parallel wallsdefines the width as being slightly greater than the width of the guideportions of the blade-like members.
 6. The underbed thread trimmer ofclaim 5 in which the guide means comprises fixed restraining meansextending into the slot, and each of the ledger blades comprises surfacemeans to engage the restraining means to hold the ledger bladessubstantially fixed, each of the ledger blades further comprising ablade slot extending in the direction of movement of the thread engagingmeans, the driving means comprising a pin extending through therespective blade slot in each of the ledger blades and engaging thelooptaker thread engaging means and the needle thread engaging means. 7.The underbed thread trimmer of claim 6 in which the pin rigidly engagesthe looptaker thread engaging means, and the blade slot through whichthe pin extends in the needle thread engaging means is shorter than therespective blade slot in each of the ledger blades.
 8. The underbedthread trimmer of claim 6 in which the needle thread engaging positionis spaced approximately three-fourths of the distance around thecircumference of the rotary hook, as measured in the direction ofrotation of the hook, from the point of closest proximity of the needleto the rotary hook.
 9. The underbed thread trimmer of claim 5 in whichthe looptaker thread engaging means comprises first and second ones ofthe blade-like members, and the first ledger blade is a third one of theblade-like members sandwiched between the first and second blade-likemembers, the needle thread engaging means comprises fourth and fifthones of the blade-like members, and the second ledger blade is a sixthone of the blade-like members sandwiched between the fourth and fifthblade-like members.
 10. The underbed thread trimmer of claim 1 in whichthe single-operation driving means comprises:spring means to drive bothof the thread engaging means to their respective thread engagingpositions; and mechanically driven means to cock the spring means and,simultaneously, to force both of the thread engaging means to theirrespective retracted positions after engaging the respective threads.11. The underbed thread trimmer of claim 10 in which the mechanicallydriven means comprises:a cam; means to rotate the cam; a cam follower tobe driven by a cam surface on the cam; and means to support the camfollower in a waiting position adjacent one part of the cam surface andto carry the cam follower into engagement with a different part of thecam surface upon actuation of the support means.
 12. The underbed threadtrimmer of claim 11 in which the mechanically driven means comprises:afirst drive shaft on which the cam is rigidly mounted to be rotated withthe first drive shaft as a unitary structure; a second drive shaftparallel to the first drive shaft; and a support member pivotallymounted on the first drive shaft and free to slide along the seconddrive shaft from a first location, which corresponds to the waitingposition and is located adjacent a predetermined part of the camsurface, to a second location, which is adjacent a distal part of thecam surface from the first part but is not entirely beyond the camsurface.
 13. The underbed thread trimmer of claim 12 in which the firstdrive shaft is a looptaker drive shaft, the second drive shaft is a feeddrive shaft, and the cam follower is a cylindrical pin pulled intocontact with the cam surface by the spring.
 14. The underbed threadtrimmer of claim 12 in which the cam is generally cylindrical, the camsurface is one surface of a slot in the cylindrical surface of the camand extends generally radially with respect to the axis of the generallycylindrical cam and substantially from one end of the cam to the other,the waiting position for the support member being adjacent the one end,the thread trimmer further comprising means to limit the travel of thecam follower longitudinally with respect to the cam by a distance notsubstantially in excess of the length of the cam.
 15. The underbedthread trimmer of claim 14 comprising, in addition:a second cam mountedon the same shaft as the first cam to rotate therewith as a unitarystructure; a release device comprising a second cam follower; a pivotedmember having a pivotal axis substantially parallel to the axes of thedrive shafts to allow the pivoted member to be pivoted between aquiescent position and an actuated position; an axle on the pivotedmember extending generally perpendicular to the pivotal axis of thepivoted member, the release device being mounted on the axle to pivotthereabout to a limited extent between a first position in which thesecond cam follower is displaced from the second cam to avoid contactbetween the second cam and the second cam follower and a second positionin which the second cam follower is aligned with the second cam,whereby, during rotation of both of the cams, the second cam pressesagainst the second cam follower to force it away from the axis of thesecond shaft; and means on the release device to press against a firstsurface of the support member in a first direction substantiallyparallel to the longitudinal axis of the second drive shaft when thepivoted member is in its quiescent position corresponding to the waitingposition of the support member, and to press against a second surface ofthe support member in a second direction at an angle to the firstdirection to pivot the support member about the first shaft to move thefirst-named cam follower radially outwardly beyond the perimeter of thefirst-named cam to allow the spring to move the support member and thefirst-named cam follower to the opposite end of the first-named cam whenthe second cam presses the second cam follower sufficiently far awayfrom the axis of the second drive shaft.
 16. The underbed thread trimmerof claim 15 comprising, in addition:a drive motor; means connecting thedrive motor to rotate both of the shafts; an arm extending from thepivoted member at an angle to the pivotal axis thereof; a solenoidcomprising a movable core connected to the arm to pivot the pivotedmember when the solenoid is energized; and a normally closed switchcomprising a pushbutton actuator positioned to be engaged by the releasedevice when the pivoted member is in a position that it occupies whenthe solenoid is not energized, the extent of movement of the pivotedmember in response to energization of the solenoid being positioned topivot the pivoted member to move the means on the release device awayfrom the first surface of the support member to allow the release deviceto pivot about the axle on the pivoted member and thereby release thepushbutton actuator of the switch; connection means connecting theswitch to the motor to cause the motor to operate when the pushbuttonactuator is released to cause both of the drive shafts to turn.
 17. Asingle operation cam arrangement comprising:a rotatable cam body; camfollower means movable between a waiting position adjacent a first partof the cam body and an actuated position adjacent a remote part of thecam body; a cam surface extending along the cam body and comprising:anentrance portion at the remote part of the cam body to engage the camfollower when the cam follower is in its actuated position and the camis rotated, and an exit end adjacent the first part of the body; and aresilient trap attached to the cam body between the other end of the camsurface and the waiting position of the cam follower, the trap beingresiliently movable to allow the cam follower to be forced past the trapby pressure of the cam surface as the cam rotates.
 18. The singleoperation cam arrangement of claim 17 in which the cam body issubstantially cylindrical and the cam surface is one generally helicalsurface of a slot extending along the cylindrical surface of the cambody.
 19. The single operation cam arrangement of claim 18 in which theresilient trap comprises an annular disc at one end of the slot, thedisc having a generally radial slot adjacent the proximal end of theslot and angularly displaced from the cam surface in the direction ofrotation of the cam.